Organic electroluminescent element, illuminator and display

ABSTRACT

An organic electroluminescent element containing an anode and a cathode having therebetween a light emitting layer, wherein the light emitting layer contains a guest compound having a substructure represented by Formula (AA): wherein A represents a group of atoms necessary to form an aromatic hydrocarbon ring or an aromatic heterocycle, B represents a group of atoms necessary to form a 5-membered aromatic heterocycle containing nitrogen or a 5-membered heterocycle containing nitrogen and M represents Ir or Pt, and a host compound represented by Formula (1):

This application is based on Japanese Patent Application No. 2005-169227filed on Jun. 9, 2005, in Japanese Patent Office, the entire content ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an organic electroluminescent element,as well as an illuminator and a display employing the same.

BACKGROUND OF THE INVENTION

As an emission type electronic display device, an electroluminescentdevice (ELD) is known. Elements constitution the ELD include aninorganic electroluminescent element and an organic electroluminescentelement (hereinafter referred to also as an organic EL element).Inorganic electroluminescent element has been used for a plane lightsource, however, a high voltage alternating current has been required todrive the element. An organic EL element has a structure in which alight emitting layer containing a light emitting compound is arrangedbetween a cathode and an anode, and an electron and a hole were injectedinto the light emitting layer and recombined to form an exciton. Theelement emits light, utilizing light (fluorescent light orphosphorescent light) generated by inactivation of the exciton, and theelement can emit light by applying a relatively low voltage, namely,several volts to several tens of volts. The element has a wide viewingangle and a high visuality since the element is of self light emissiontype. Further, the element is a thin, complete solid element, therefore,the element is noted from the viewpoint of space saving and portability.

For the practical use in the future, an organic EL element is desired toemit light of high luminance with high efficiency at a lower power.

For example, disclosed is an organic EL element exhibiting higherluminance of emitting light with longer life in which a stilbenederivative, a distyrylarylene derivative or a tristyrylarylenederivative doped with a slight amount of a fluorescent compound isemployed (refer to Japanese Patent No. 3093796).

Also known are: an organic EL element which has an organic lightemitting layer containing 8-hydroxyquinoline aluminum complex as a hostcompound doped with a slight amount of a fluorescent compound (forexample, refer to Japanese Patent Publication Open to Public Inspection(hereafter referred to as JP-A) No. 63-264692); and an organic ELelement which has an organic light emitting layer containing8-hydroxyquinoline aluminum complex as a host compound doped with aquinacridone type dye (for example, refer to JP-A No. 3-255190).

When light emitted through excited singlet state is used in the organicEL element as disclosed in the above Patent documents, the upper limitof the external quantum efficiency (ηext) is considered to be at most5%, because the generation probability of excited species capable ofemitting light is 25%, since the generation ratio of singlet excitedspecies to triplet excited species is 1:3, and further, external lightemission efficiency is 20%.

Since an organic EL element, employing phosphorescence through theexcited triplet, has been reported by Prinston University (refer to M.A. Baldo et al., nature, 395, 151-154(1998)), studies on materialsemitting phosphorescence at room temperature have been actively carriedout.

Examples are also reported in M. A. Baldo et al., Nature, 403(17),750-753(2000) or in U.S. Pat. No. 6,097,147.

As the upper limit of the internal quantum efficiency of the excitedtriplet is 100%, the light emission efficiency of the exited triplet istheoretically four times higher than that of the excited singlet.Accordingly, light emission employing the excited triplet may enablealmost the same performance as a cold cathode tube, and it is attractingattention to be applied as an illuminator.

For example, S. Lamansky et al., J. Am. Chem. Soc., 123, 4304 (2001)reports that many kinds of heavy metal complexes such as iridiumcomplexes have been synthesized and studied.

In above mentioned M. A. Baldo et al., Nature, 403(17), 750-753 (2000),an example employing tris(2-phenylpyridine)iridium as a dopant has beenstudied.

As other examples, M. E. Tompson et al. have reported the application ofL₂Ir(acac) such as (ppy)₂Ir(acac) as a dopant in the 10th InternationalWorkshop on Inorganic and Organic Electroluminescence (EL '00,Hamamatsu), and Moon-Jae Youn. 0 g, Tetsuo Tsutsui et al., have reportedthe application of tris(2-(p-tolyl)pyridine)iridium (Ir(ptpy)₃), andtris(benzo[h]quinoline)iridium (Ir(bzq)₃) as a dopant in the 10thInternational Workshop on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu). These metal complexes are generally referred to as anortho metalated iridium complex.

Also in aforementioned S. Lamansky et al., J. Am. Chem. Soc., 123, 4304(2001), an application of various iridium complexes to an organic ELelements has been examined.

In order to obtain a higher emission efficiency, Ikai et al. havereported an application of a hole transport compound as a host materialof a phosphorescent compound in the 10th International Workshop onInorganic and Organic Electroluminescence (EL '00, Hamamatsu). Also, M.E. Tompson et al., have reported an application of variouselectron-transport compounds as a host material of a phosphorescentcompound, which is further doped with a novel iridium complex.

An ortho metalated complex having platinum as a central metal instead ofiridium is also attracting attention. Many examples of this type ofcomplex having a characteristic ligand have been known (for example,refer to Patent Documents 1-5).

Since each of the above examples is related to phosphorescent emission,the luminance, and the emission efficiency are notably improved comparedto the conventional organic EL elements, however, the emission life ofeach element have been shorter than those of the conventional organic ELelements. It has not been fully easy to overcome the problem of a highemission efficiency phosphorescent material that the emission wavelengthtends to shift to a shorter wavelength range and that the emission lifeof the organic EL element is not fully long, and a fully satisfactoryperformance for the practical use has not been obtained.

As a material to improve the performance, known is an iridium complex ora platinum complex each having a phenyl imidazole derivative as a ligand(for example, refer to Patent Documents 6-8). However, the emissionefficiencies exhibited by these complexes are not fully satisfactory,and a further improvement has been desired.

Patent Document 1 Japanese Patent Publication Open to Public Inspection(hereafter referred to as JP-A) No. 2002-332291 Patent Document 2 JP-ANo. 2002-332292 Patent Document 3 JP-A No. 2002-338588 Patent Document 4JP-A No. 2002-226495 Patent Document 5 JP-A No. 2002-234894 PatentDocument 6 WO 02/15645 Patent Document 7 WO 05/7767 Patent Document 8JP-A No. 2005-68110

SUMMARY OF THE INVENTION

An object of the present invention is to provide an organic EL elementexhibiting a controlled emission wavelength, a high emission efficiencyand a long life, and to provide an illuminator and a display using theorganic EL element.

One of the aspects of the present invention is an organicelectroluminescent element containing an anode, a cathode and havingtherebetween a light emitting layer, wherein the light emitting layercontains a guest compound having a substructure represented by Formula(AA): wherein A represents a group of atoms necessary to form anaromatic hydrocarbon ring or an aromatic heterocycle, B represents agroup of atoms necessary to form a 5-membered aromatic heterocyclecontaining nitrogen or a 5-membered heterocycle containing nitrogen andM represents Ir or Pt, and a host compound represented by Formula (1):wherein Ra₁ represents an alkyl group, an alkenyl group, an alkynylgroup, a cycloalkyl group, an aromatic hydrocarbon group, an aromaticheterocyclic group or a heterocyclic group, R₁, R₂ and R₅ each representa hydrogen atom or a substituent, and n1, n2 and n5 each represent aninteger of 0 to 4.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a display having organic ELelements.

FIG. 2 is a view showing display section A.

FIG. 3 illustrates an equivalent circuit of a driving circuit whichdrives a pixel.

FIG. 4 is a view showing a passive matrix display.

FIG. 5 is a schematic illustration of an illuminator.

FIG. 6 is a cross-section view showing an illuminator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above object of the present invention is achieved by the followingstructures.

-   (1) An organic electroluminescent element containing an anode and a    cathode having therebetween a light emitting layer, wherein the    light emitting layer contains a guest compound having a substructure    represented by Formula (AA) and a host compound represented by    Formula (1):

wherein A represents a group of atoms necessary to form an aromatichydrocarbon ring or an aromatic heterocycle, B represents a group ofatoms necessary to form a 5-membered aromatic heterocycle containingnitrogen or a 5-membered heterocycle containing nitrogen and Mrepresents Ir or Pt,

wherein Ra₁ represents an alkyl group, an alkenyl group, an alkynylgroup, a cycloalkyl group, an aromatic hydrocarbon group, an aromaticheterocyclic group or a heterocyclic group, R₁, R₂ and R₅ each representa hydrogen atom or a substituent, and n1, n2 and n5 each represent aninteger of 0 to 4.

-   (2) The organic electroluminescent element of Item (1), wherein the    guest compound is represented by Formula (A):

wherein Ra represents a hydrogen atom, an alkyl group, an alkenyl group,an alkynyl group, a cycloalkyl group, an aromatic hydrocarbon group, anaromatic heterocyclic group or a heterocyclic group, Rb and Rc eachrepresent a hydrogen atom or a substituent, A1 represents a group ofatoms necessary to form an aromatic hydrocarbon ring or an aromaticheterocycle, M represents Ir or Pt.

-   (3) The organic electroluminescent element of Item (1), wherein the    guest compound is represented by Formula (B):

wherein Ra represents a hydrogen atom, an alkyl group, an alkenyl group,an alkynyl group, a cycloalkyl group, an aromatic hydrocarbon group, anaromatic heterocyclic group or a hetertocyclic group, Rb, Rc, Rb₁ andRc₁ each represent a hydrogen atom or a substituent, A1 represents agroup of atoms necessary to form an aromatic hydrocarbon ring or anaromatic heterocycle, M represents Ir or Pt.

-   (4) The organic electroluminescent element of Item (1), wherein the    guest compound is represented by Formula (C):

wherein, Ra represents a hydrogen atom, an alkyl group, an alkenylgroup, an alkynyl group, a cycloalkyl group, an aromatic hydrocarbongroup, an aromatic heterocyclic group or a heterocyclic group, Rb, andRc each represent a hydrogen atom or a substituent, A1 represents agroup of atoms necessary to form an aromatic hydrocarbon ring or anaromatic heterocycle, M represents Ir or Pt.

-   (5) The organic electroluminescent element of Item (1), wherein the    host compound is represented by Formula (2): Formula (2)

wherein R₁ to R₅ each represent a substituent and n1 to n5 eachrepresent an integer of 0 to 4.

-   (6) The organic electroluminescent element of Item (1), wherein the    host compound is represented by Formula (3):

wherein R₁-R₄, R₆ and R₇ each represent a substituent; n1 to n4 eachrepresent an integer of 0 to 4; n6 and n7 each represent an integer of 0to 3; and RA and RB each represent a substituent.

-   (7) The organic electroluminescent element of any one of Items (2)    to (4), wherein the aromatic hydrocarbon ring represented by A1    Formula (A) is a benzene ring.-   (8) The organic electroluminescent element of any one of Items (2)    to (4), wherein the guest compound represented by Formula (A) is a    tris-form.-   (9) The organic electroluminescent element of any one of Items (1)    to (8) emitting blue light.-   (10) The organic electroluminescent element of any one of Items (1)    to (8) emitting white light.-   (11) A display containing the organic electroluminescent element of    any one of Items (1) to (10).-   (12) An illuminator containing the organic electroluminescent    element of any one of Items (1) to (10).-   (13) A display containing the illuminator of Item (12) and a liquid    crystal cell as a display means.

According to the present invention, obtained is an organic EL elementexhibiting a controlled emission wavelength, a high emission efficiencyand a long life, as well as an illuminator and a display using theorganic EL element.

It was found in the present invention that, when a guest compound (alsoreferred to as a emitting dopant) having a substructure represented byFormula (AA) is used in combination with a host compound represented byFormula (1), an excellent emission efficiency and long life of theorganic EL element is attained.

Namely, it was found in the present invention that, when an organic ELelement was designed so as to contain, in the emitting layer, a guestcompound (also referred to as a emitting dopant) having a substructurerepresented by Formula (AA) together with a host compound represented byFormula (1), an excellent emission efficiency and long life of theorganic EL element was attained. It was also found that a highlyefficient display and an illuminator were obtained by using the organicEL element of the present invention.

The host compound represented by Formula (1) of the present inventionwill now be explained.

In the present invention, as a host compound, the compound representedby the above Formula (1) is preferable, and as a compound represented byFormula (1), the compound represented by the above Formula (2) or (3) ismore preferable.

Examples of an alkyl group represented by Ra₁ in Formula (1) include: amethyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, an isopentyl group, a 2-ethylhexyl group, an octyl group, anundecyl group, a dodecyl group and a tetradecyl group. These groups mayfurther have a substituent represented by R₁, R₂, or R₅ in Formula (1),which will be explained later.

Examples of an alkenyl group represented by Ra₁ in Formula (1) include:a vinyl group, an allyl group, a 1-propenyl group, a 2-butenyl group, a1,3-butadienyl group, a 2-pentenyl group and an isopropenyl group. Thesegroups may further have a substituent represented by R₁, R₂, or R₅ inFormula (1), which will be explained later.

Examples of an alkynyl group represented by Ra₁ in Formula (1) include:an ethynyl group and a propargyl group. These groups may further have asubstituent represented by R₁, R₂, or R₅ in Formula (1), which will beexplained later.

Examples of a cycloalkyl group represented by Ra₁ in Formula (1)include: a cyclopentyl group and a cyclohexyl group. These groups mayfurther have a substituent represented by R₁, R₂, or R₅ in Formula (1),which will be explained later.

Examples of an aromatic hydrocarbon group (also referred to as anaromatic ring group or an aryl group) represented by Ra₁ in Formula (1)include: a phenyl group, a tolyl group, an azulenyl group, an anthranylgroup, a phenanthryl group, a pyrenyl group, a chrysenyl group, anaphthacenyl group, an o-terphenyl group, a m-terphenyl group, apara-terphenyl group, an acenaphthenyl, a coronenyl group, a fluorenylgroup and a pertlenyl group. These groups may further have a substituentrepresented by R₁, R₂, or R5 in Formula (1), which will be explainedlater.

Examples of an aromatic heterocycle group represented by Ra₁ in Formula(1) include: a pyrrolyl group, a furyl group, a thienyl group, a pyridylgroup, a pyridazinyl group, a pyrimidinyl group, a pyrazinyl group, atriazinyl group, an indolyl group, an indolizinyl group, an imidazolylgroup, a pyrazolyl group, a thiazolyl group, a thiadiazinyl group, anoxadiazorinyl group, a benzoquinolinyl group, a thiadiazolyl group, aquinolinyl group, a quinazolinyl group, an oxadiazolyl group, abenzoquinolinyl group, a thiadiazolyl group, a pyrrolothiazolyl group, apyrrolopyridazinyl group, a tetrazolyl group, an oxazolyl group, acarbazolyl group, a carbolinyl group, a diazacarbazolyl group (in whichone of the carbon atoms which constitute the carboline ring of the abovecarbolinyl group is replaced with a nitrogen atom) and a phthalazinylgroup. These groups may further have a substituent represented by R₁,R₂, or R₅ in Formula (1), which will be explained later.

Examples of a heterocycle group represented by Ra₁ in Formula (1)include: a pyrrolidyl group, an imidazolysyl group, an morpholyl groupand an oxazolisyl group. These groups may further have a substituentrepresented by R₁, R₂, or R₅ in Formula (1), which will be explainedlater.

Examples of substituents represented R₁, R₂ and R₅ in Formula (1)include: an alkyl group (for example, a methyl group, an ethyl group, apropyl group, an isopropyl group, a tert-butyl, a pentyl group, a hexylgroup, an octyl group, a dodecyl group, a tridecyl group, a tetradecylgroup and a pentadecyl group); cycloalkyl groups (for example, acyclopentyl group and a cyclohexyl group); alkenyl groups (for example,a vinyl group and an allyl group); alkynyl groups (for example, anethynyl group and a propargyl group); aromatic hydrocarbon groups (alsoreferred to as an aromatic ring group or an aryl group, for example, aphenyl group and a naphthyl group); aromatic heterocycle groups (forexample, a furyl group, a thienyl group, a pyridyl group, a pyridazinylgroup, pyrimidinyl group, a pyrazinyl group, a triazinyl group, animidazolyl group, a pyrazolyl group, a thiazolyl group, a quinazolinylgroup and a phthalazinyl group); heterocycle groups (for example, apyrrolidyl group, an imidazolysyl group, a morpholyl group and anoxazolisyl group); alkoxy groups (for example, a methoxy group, anethoxy group, a propyloxy group, a pentyloxy group, a hexyloxy group, anoctyloxy group and a dodecyl oxygroup); cycloalkoxyl groups (forexample, a cyclopentyloxy group and a cyclohexyloxy group); aryloxygroups (for example, a phenoxy group and a naphthyloxy group); alkylthiogroups (for example, a methylthio group, an ethylthio group, apropylthio group, a pentylthio group, a hexylthio group, an octylthiogroup and a dodecylthio group); cycloalkylthio groups (for example, acyclopentylthio group and a cyclohexylthio group); arylthio groups (forexample, a phenylthio group and a naphthylthio group); alkoxycarbonylgroups (for example, a methyloxycarbonyl group, an ethyloxycarbonylgroup, a butyloxycarbonyl group, an octyloxycarbonyl group and adodecyloxycarbonyl group); aryloxycarbonyl groups (for example, aphenyloxycarbonyl group and a naphthyloxycarbonyl group); sulfamoylgroup (for example, an aminosulfonyl group, a methylaminosulfonyl group,a dimethylaminosulfonyl group, a butylaminosulfonyl group, ahexylaminosulfonyl group, a cyclohexylaminosulfonyl group, anoctylaminosulfonyl group, a dodedylaminosulfonyl group, aphenylaminosulfonyl group, a naphthylaminosulfonyl group and a2-pyridylaminosulfonyl group); acyl groups (for example, an acetylgroup, an ethylcarbonyl group, a propylcarbonyl group, a pentylcarbonylgroup, a cyclohexylcarbonyl group, an octylcarbonyl group, a2-ethylhexylcarbonyl group, a dodecylcarbonyl group, a phenylcarbonylgroup, a naphthylcarbonyl group and a pyridylcarbonyl group); acyloxygroups (for example, an acetyloxy group, an ethylcarbonyloxy group, abutylcarbonyloxy group, an octylcarbonyloxy group, a dodecylcarbonyloxygroup and a phenylcarbonyloxy group); amide groups (for example, amethylcarbonylamino group, an ethylcarbonylamino group, adimethylcarbonylamino group, a propylcarbonylamino group, apentylcarbonylamino group, a cyclohexylcarbonylamino group, a2-ethylhexylcarbonylamino group, an octylcarbonylamino group, adodecylcarbonylamino group, a phenylcarbonylamino group and anaphthylcarbonylamino group); carbamoyl groups (for example, anaminocarbonyl group, a methylaminocarbonyl group, adimethylaminocarbonyl group, a propylaminocarbonyl group, apentylaminocarbonyl group, a cyclohexylaminocarbonyl group, anoctylaminocarbonyl group, a 2-ethylhexylaminocarbonyl group, adodecylaminocarbonyl group, a phenylaminocarbonyl group, anaphthylaminocarbonyl group and a 2-pyridyaminocarbonyl group); ureidogroups (for example, a methylureido group, an ethylureido group, apentylureido group, a cyclohexylureido group, an octylureido group, adodecylureido group, a phenylureido group, a naphthylureido group and a2-pyridyl amino ureido group); sulfinyl groups (for example, amethylsulfinyl group, an ethylsulfinyl group, a butylsulfinyl group, acyclohexylsulfinyl group, a 2-ethylhexylsulfinyl group, adodecylsulfinyl group, a phenylsulfinyl group, a naphthylsulfinyl groupand a 2-pyridylsulfinyl group); alkylsulfonyl groups (for example, amethylsulfonyl group, an ethylsulfonyl group, a butylsulfonyl group, acyclohexylsulfonyl group, a 2-ethylhexylsulfonyl group and adodecylsulfonyl group); arylsulfonyl groups (for example, aphenylsulfonyl group, a naphthylsulfonyl group and a 2-pyridylsulfonylgroup); amino groups (for example, an amino group, an ethylamino group,a dimethylamino group, a butylamino group, a cyclopentylamino group, a2-ethylhexylamino group, a dodecylamino group, an anilino group, anaphthylamino group and a 2-pyridylamino group); halogen atoms (forexample, a fluorine atom, a chlorine atom and a bromine atom);hydrofluorocarbon groups (for example, a fluoromethyl group, atrifluoromethyl group, a pentafluoroethyl group and a pentafluorophenylgroup); a cyano group; a nitro group; a hydroxyl group; a mercaptogroup; and silyl groups (for example, a trimethylsilyl group, atriisopropylsilyl group, a triphenylsilyl group and a phenyldiethylsilylgroup). These groups may further be replaced with the above-mentionedsubstituent.

The substituents represented by R₁-R₇, RA and RB in Formulas (2) and (3)are common to those represented by R₁, R₂ and R₅ in Formula (1).

Specific examples of a host compound represented by Formula (1), (2) or(3) are shown below, however, the present invention is not limitedthereto.

Guest compounds (also referred to as emission dopants) of the presentinvention having substructures represented by Formula (AA), (A), (B), or(C) will now be explained.

In Formulas (AA), (A), (B) and (C), A and A1 each represent an atomicgroup forming an aromatic hydrocarbon ring or an aromatic heterocycle.Examples of the aromatic hydrocarbon ring include: a benzene ring, abiphenyl ring, a naphthalene ring, an azulene ring, an anthracene ring,A phenanthrene ring, a pyrene ring, a chrysene ring, a naphthacene ring,a triphenylene ring, an o-terphenyl ring, a m-terphenyl ring, ap-terphenyl ring, an acenaphthene ring, a coronene ring, a fluorenering, a fluoroanthrene ring, a naphthacene ring, a penthacene ring, aperylene ring, a pentaphene ring, a picene ring, a pyrene ring, thePyranthrene ring and an anthranthrene ring. Examples of the aromaticheterocycle include: a furan ring, a thiophene ring, a pyridine ring, apyridazine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, abenzimidazole ring, an oxadiazole ring, a triazole ring, an imidazolering, a pyrazole ring, a thiazole ring, an indole ring, a benzimidazolering, a benzothiazole ring, a benzoxazole ring, a quinoxaline ring, aquinazoline ring, a phthalazine ring, a carbazole ring, a carboline ringand a diazacarbazole ring (in which one of the carbon atoms of thehydrocarbon ring which constitutes a carboline ring is further replacedby a nitrogen atom).

In Formulas (A), (B) and (C), Ra represent a hydrogen atom, an alkylgroup, an alkenyl group, an alkynyl group, a cycloalkyl group, anaromatic hydrocarbon group, an aromatic heterocycle group, or aheterocycle group, and Rb, Rc, Rb₁, and Rc₁, each represent a hydrogenatom or a substituent, wherein Ra is common to Ra₁ in Formula (1). Thesubstituents represented by Rb, Rc, Rb₁, or Rc₁, are common to thesubstituents represented by R₁, R₂ or R₅ in Formula (1).

The structure represented by each of Formula (AA), (A), (B) and (C) is asubstructure and needs one or more ligand according to the valence ofthe central metal to complete the structure as an emission dopant.Examples of the ligand include: a halogen atom (for example, a fluorineatom, a chlorine atom, a bromine atom, or an iodine atom), an aromatichydrocarbon group (also referred to as an aromatic hydrocarbon ringgroup or an aryl group, for example, a phenyl group, a p-chlorophenylgroup, a mesityl group, a tolyl group, a xylyl group, a biphenyl group,a naphthyl group, an anthryl group and a phenanthryl group), an alkylgroup (for example, a methyl group, an ethyl group, an isopropyl group,and a hydroxyethyl group, a methoxymethyl group, a trifluoromethyl groupand t-butyl group), an alkyloxy group, an aryloxy group, an alkylthiogroup, an arylthio group, an aromatic heterocycle group (for example, afuryl group, a thienyl group, a pyridyl group, a pyridazinyl group, anda pyrimidinyl group, a pyrazinyl group, a triazinyl group, an imidazolylgroup, a pyrazolyl group, a thiazolyl group, a quinazolinyl group, acarbazolyl group, a carbolinyl group and a phthalazinyl group) and asubstructure represented by Formula (AA), (A), (B), or (C), from whichcentral metal M is removed.

In Formulas (A)-(C), M represents Ir or Pt, and specifically, Ir ispreferable. Moreover, preferable is a tris-form including thesubstructures represented by Formula (A), (B) or (C).

Examples of the guest compounds (also referred to as emission dopants)of the present invention having a substructure represented by aboveFormula (AA), (A), (B) or (C) are shown below, however, the presentinvention is not limited thereto.

A synthetic example of a compound having the substructure represented byFormula (AA), (A), (B), or (C) of the present invention will be shown.

Example of Synthesis of D-1:

Example of Synthesis

In a three necked 500 ml flask, (i) 4.0 g of D-1acac, 2.6 g ofphenylimidazole and 300 ml of glycerin were charged, (ii) a thermometerand the a condenser tube were attached, (iii) the flask was set on theoil bath equipped with a stirrer, (iv) bath temperature was graduallyincreased and then adjusted so that the inside temperature was kept at150° C., (v) the content was kept agitating for 5 hours to complete thereaction, (vi) deposition of crystals were observed when the product wascooled to room temperature, (vii) the product was diluted with 200 ml ofmethanol, (viii) the crystals were separated by filtering, washed withmethanol, and dried to obtain 1.6 g (36.5%) of the product. The crystalwas identified to be D-1 by using ¹H-NMR (nuclear magnetic resonancespectral method) and MS (mass spectrometry).

Details of the constituting layers of an organic EL element of thepresent invention will now be explained. Examples of preferableconstituting layer of the organic EL element are shown below, however,the present invention is not limited thereto.

-   (i): Anode/Light emitting layer/Electron transporting layer/Cathode-   (ii): Anode/Hole transporting layer/Light emitting layer/Electron    transporting layer/Cathode-   (iii): Anode/Hole transporting layer/Light emitting layer/Hole    blocking layer/Electron transporting layer/Cathode-   (iv): Anode/Hole transporting layer/Light emitting layer/Hole    blocking layer/Electron transporting layer/Cathode buffer    layer/Cathode-   (v): Anode/Anode buffer layer/Hole transporting layer/Light emitting    layer/Hole blocking layer/Electron transporting layer/Cathode buffer    layer/Cathode    <<Anode>>

For the anode of the organic EL element, a metal, an alloy, or anelectroconductive compound each having a high working function (not lessthan 4 eV), and mixture thereof are preferably used as the electrodematerial. Specific examples of such an electrode material include ametal such as Au, CuI and a transparent electroconductive material suchas indium tin oxide (ITO), SnO₂, or ZnO. A material capable of formingan amorphous and transparent conductive layer such as IDIXO (In₂O₃—ZnO)may also be used. The anode may be prepared by forming a thin layer ofthe electrode material according to a depositing or spattering method,and by forming the layer into a desired pattern according to aphotolithographic method. When required precision of the pattern is notso high (not less than 100 μm), the pattern may be formed by depositingor spattering of the electrode material through a mask having a desiredform. When light is emitted through the anode, the transmittance of theanode is preferably 10% or more, and the sheet resistance of the anodeis preferably not more than several hundred Ω/□. The thickness of thelayer is ordinarily within the range of from 10 to 1000 nm, andpreferably from 10 to 200 nm, although it may vary due to kinds ofmaterials used.

<<Cathode>>

On the other hand, for the cathode, a metal (also referred to as anelectron injecting metal), an alloy, and an electroconductive compoundeach having a low working function (not more than 4 eV), and a mixturethereof are used as the electrode material. Specific examples of such anelectrode material include sodium, sodium-potassium alloy, magnesium,lithium, a magnesium/copper mixture, a magnesium/silver mixture, amagnesium/aluminum mixture, magnesium/indium mixture, analuminum/aluminum oxide (Al₂O₃) mixture, indium, a lithium/aluminummixture, and a rare-earth metal. Among them, a mixture of an electroninjecting metal and a metal higher in the working function than that ofthe electron injecting metal, such as the magnesium/silver mixture,magnesium/aluminum mixture, magnesium/indium mixture, aluminum/aluminumoxide (Al₂O₃) mixture, lithium/aluminum mixture, or aluminum is suitablefrom the view point of the electron injecting ability and resistance tooxidation. The cathode can be prepared forming a thin layer of such anelectrode material by a method such as a deposition or spatteringmethod. The sheet resistance as the cathode is preferably not more thanseveral hundred Ω/□, and the thickness of the layer is ordinarily from10 nm to 5 μm, and preferably from 50 to 200 nm. It is preferable inincreasing the light emission efficiency that either the anode or thecathode of the organic EL element is transparent or semi-transparent.

After a layer of the metal described above as a cathode is formed togive a thickness of from 1 to 20 nm, a layer of the transparentelectroconductive material as described in the anode may be formed onthe resulting metal layer, whereby a transparent or semi-transparentcathode can be prepared. Employing the cathode, an organic EL elementcan be manufactured in which both anode and cathode are transparent.

Injecting layer, blocking layer, electron transporting layer will now beexplained.

<<Injecting Layer: Electron Injecting Layer, Hole Injecting Layer>>

The injecting layer is optionally provided, for example, an electroninjecting layer or a hole injecting layer, and may be provided betweenthe anode and the light emitting layer or hole transporting layer, andbetween the cathode and the light emitting layer or electrontransporting layer as described above.

The injecting layer herein referred to is a layer provided between theelectrode and the organic layer in order to reduce the driving voltageor to improve of light emission efficiency. As the injecting layer thereare a hole injecting layer (an anode buffer layer) and an electroninjecting layer (a cathode buffer layer), which are described in“Electrode Material” pages 123-166, Div. 2 Chapter 2 of “Organic ELelement and its frontier of industrialization” (published by NTSCorporation, Nov. 30, 1998) in detail.

The anode buffer layer (hole injecting layer) is described in, forexample, JP-A Nos. 9-45479, 9-260062, and 8-288069, and its examplesinclude a phthalocyanine buffer layer represented by a copperphthalocyanine layer, an oxide buffer layer represented by a vanadiumoxide layer, an amorphous carbon buffer layer, a polymer buffer layeremploying and an electroconductive polymer such as polyaniline(emeraldine) and polythiophene.

The cathode buffer layer (electron injecting layer) is described in, forexample, JP-A Nos. 6-325871, 9-17574, and 10-74586, in detail, and itsexamples include a metal buffer layer represented by a strontium oraluminum layer, an alkali metal compound buffer layer represented by alithium fluoride layer, an alkali earth metal compound buffer layerrepresented by a magnesium fluoride layer, and an oxide buffer layerrepresented by an aluminum oxide. The buffer layer (injecting layer) ispreferably very thin and has a thickness of preferably from 0.1 to 5 μmdepending on kinds of the material used.

<<Blocking Layer: Hole Blocking Layer, Electron Blocking Layer>>

The blocking layer is a layer provided if necessary in addition to thefundamental component layers as described above, and is for example ahole blocking layer as described in JP-A Nos. 11-204258, and 11-204359,and on page 237 of “Organic EL element and its frontier ofindustrialization” (published by NTS Corporation, Nov. 30, 1998).

The hole blocking layer is an electron transporting layer in a broadsense, and is a material having an ability of transporting electrons,however, an extremely poor ability of transporting holes, which canincrease a recombination probability of electrons and holes bytransporting electrons while blocking holes.

The hole blocking layer of the organic EL element of the presentinvention is provided adjacent to the light emitting layer.

In the present invention, the hole blocking layer preferably containsthe above mentioned compounds relating the present invention as a holeblocking material, whereby an organic EL element exhibiting a higheremission efficiency is obtained, further an organic EL elementexhibiting a longer life is obtained.

On the other hand, the electron blocking layer is an hole transportinglayer in a broad sense, and is a material having an ability oftransporting holes, however, an extremely poor ability of transportingelectrons, which can increase a recombination probability of electronsand holes by transporting holes while blocking electrons.

<<Light Emitting Layer>>

The light emitting layer of the present invention is a layer whereelectrons and holes, injected from electrodes, an electron transportinglayer or a hole transporting layer, are recombined to emit light. Theportions where light is emitted may be in the light emitting layer or atthe interface between the light emitting layer and the layer adjacentthereto.

(Host Compounds)

The light emitting layer of the present invention preferably contains ahost compound and an emitting dopant (also referred to as aphosphorescent light emitting compound) described above. In the presentinvention, the above described compounds relating to the presentinvention are preferably used as a host compound, whereby an organic ELelement exhibiting higher emission efficiency is obtained. Further,other compounds besides the relating compounds to the present inventionmay also be used as a host compound.

In the present invention, a host compound is defined as a compound ofwhich the quantum yield of phosphorescent light emission is less than0.01 at 25° C.

A plurality of known host compounds may also be used in combination. Useof a plurality of host compounds makes the control of the transfer ofelectrons possible, and an organic EL element exhibiting higher lightemission efficiency is obtained. Also, use of a plurality ofphosphorescent compounds makes it possible to mix different colors ofemitted light, and an arbitrary color of emitted light is obtained.Emission of white light is possible by adjusting the types and amountsof doping of mixed phosphorescent compounds, whereby application of theorganic EL element to an illuminator or a backlight is possible.

Among the known host compounds, preferable are the compounds having holetransporting ability, electron transporting ability, effect to prevent ashift of light emission to a longer wavelength side and a high Tg (aglass transition temperature).

Examples of the known host compounds include the compounds disclosed inthe following documents:

JP-A No. 2001-257076, No. 2002-308855, No. 2001-313179, No. 2002-319491,No. 2001-357977, No. 2002-334786, No. 2002-8860, No. 2002-334787, No.2002-15871, No. 2002-334788, No. 2002-43056, No. 2002-334789, No.2002-75645, No. 2002-338579, No. 2002-105445, No. 2002-343568, No.2002-141173, No. 2002-352957, No. 2002-203683, No. 2002-363227, No.2002-231453, No. 2003-3165, No. 2002-234888, No. 2003-27048, No.2002-255934, No. 2002-260861, No. 2002-280183, No. 2002-299060, No.2002-302516, No. 2002-305083, No. 2002-305084, No. 2002-308837.

The light emitting layer may contain a host compound having afluorescence maximum wavelength as a host compound. In this case, by aenergy transfer from other host compound or a phosphorescent compound toa fluorescent compound, light emission from a host compound having afluorescence maximum wavelength is obtained as the result ofelectroluminescence of an organic EL element. The host compound having afluorescence maximum wavelength preferably has a high fluorescencequantum yield in the form of solution. Herein, the fluorescence quantumyield is preferably not less than 10%, and more preferably not less than30%. Examples of the a host compound having a wavelength providing afluorescence maximum wavelength include a coumarin dye, a cyanine dye, achloconium dye, a squalenium dye, an oxobenzanthracene dye, afluorescene dye, a rhodamine dye, a pyrylium dye, a perylene dye, astilbene dye, and a polythiophene dye. The fluorescence quantum yieldcan be measured according to a method described in the fourth edition,Jikken Kagaku Koza 7, Bunko II, p. 362 (1992) published by Maruzen.(Guest Compounds (also referred to as Emitting Dopant))

The guest compound (also referred to as Emitting Dopant) of the presentinvention is a compound which emits light from the excited triplet,which can emit phosphorescence at room temperature (25° C.), andexhibits a phosphorescent quantum yield at 25° C. of not less than 0.01.The phosphorescent quantum yield at 25° C. is preferably not less than0.1. The phosphorescent quantum yield can be measured according to amethod described in the fourth edition “Jikken Kagaku Koza 7”, Bunko II,page 398 (1992) published by Maruzen. The phosphorescent quantum yieldcan be measured in a solution employing various kinds of solvents. Theguest compound used of the present invention is a compound, in which thephosphorescent quantum yield measured employing any one of the solventsfalls within the above-described range.

The light emission of the guest compound is divided in two types inprinciple, one is an energy transfer type in which recombination of acarrier occurs on the host to which the carrier is transported to excitethe host, the resulting energy is transferred to the phosphorescentcompound, and light is emitted from the phosphorescent compound, and theother is a carrier trap type in which recombination of a carrier occurson the phosphorescent compound which is a carrier trap material, andlight is emitted from the phosphorescent compound. However, in eachtype, energy level of the phosphorescent compound in excited state islower than that of the host in excited state.

In addition to the guest compounds of the present invention having asubstructure represented by Formula (AA), (A), (B) (C), a known guestcompound, for example, listed below may be used in combination.

These compounds can be synthesized according to a method described inInorg. Chem., 40, 1704-1711.

In the present invention, the wavelength of the phosphorescence maximumof the phosphorescent compound is not specifically limited.Theoretically, the phosphorescence wavelength can be varied by selectinga center metal, a ligand, or a substituent of the ligand. Thephosphorescent compound preferably has a wavelength of thephosphorescence maximum in the wavelength region from 380 to 480 nm.Such an organic EL element emitting a blue or white lightphosphorescence can provide higher emission efficiency.

Color of light emitted from the organic EL element or the compound ofthe present invention is measured by a spectral radiance meter CS-1000,manufactured by Konica Minolta Sensing Inc., and expressed according toCIE chromaticity diagram described in FIG. 4.16 on page 108 of “ShinpenShikisai Kagaku Handbook” (Coloring Science Handbook, New Edition),edited by Nihon Shikisai Gakkai, published by Todai Shuppan Kai, 1985.

The light emitting layer can be formed employing the above-describedcompounds and a known method such as a vacuum deposition method, a spincoat method, a casting method, an LB method or an ink jet method. Thethickness of the light emitting layer is not specifically limited,however, is ordinarily from 5 nm to 5 μm, and preferably from 5 to 200nm. The light emitting layer may be composed of a single layercontaining one or two or more of the phosphorescent compound or the hostcompound, or of plural layers containing the same composition ordifferent composition.

<<Hole Transporting Layer>>

The hole transporting layer contains a material having a holetransporting ability, and in a broad sense a hole injecting layer or anelectron blocking layer are included in a hole transporting layer.

The hole transporting layer may be either an organic substance or aninorganic substance as long as it has a hole injecting ability, a holetransporting ability or an ability to form a barrier to electrons.Examples thereof include a triazole derivative, an oxadiazolederivative, an imidazole derivative, a polyarylalkane derivative, apyrazoline derivative and a pyrazolone derivative, a phenylenediaminederivative, an arylamine derivative, an amino substituted chalconederivative, an oxazole derivative, a styryl anthracene derivative, afluorenone derivative, a hydrazone derivative, a stilbene derivative, asilazane derivative, an aniline based copolymer, and anelectroconductive oligomer, specifically a thiophene oligomer.

As the hole transporting material, those described above are used,however, a porphyrin compound, an aromatic tertiary amine compound or astyrylamine compound is preferably used, and, specifically, an aromatictertiary amine compound is more preferably used.

Typical examples of the aromatic tertiary amine compound and styrylaminecompound include N,N,N′,N′-tetraphenyl-4,4′-diaminophenyl,N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(TPD), 2,2-bis(4-di-p-tolylaminophenyl)propane,1,1-bis(4-di-p-tolylaminophenyl)cyclohexane,N,N,N′,N′-tetra-p-tolyl-4,4′-diaminobiphenyl,1,1-bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane,bis(4-dimethylamino-2-methylphenyl)phenylmethane,bis(4-di-p-tolylaminophenyl)phenylmethane,N,N′-diphenyl-N,N′-di(4-methoxyphenyl)-4,4′-diaminobiphenyl,N,N,N′,N′-tetraphenyl-4,4′-diaminodiphenylether,4,4′-bis(diphenylamino)quardriphenyl, N,N,N-tri(p-tolyl)amine,4-(di-p-tolylamino)-4′-[4-(di-p-tolylamino)styryl]stilbene,4-N,N-diphenylamino-(2-diphenylvinyl)benzene,3-methoxy-4′-N,N-diphenylaminostylbene, N-phenylcarbazole, compoundsdescribed in U.S. Pat. No. 5,061,569 which have two condensed aromaticrings in the molecule thereof such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD), and compoundsdescribed in JP-A No. 4-308688 such as4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]-triphenylamine (MTDATA)in which three triphenylamine units are bonded in a starburst form.

A polymer in which the material mentioned above is introduced in thepolymer chain or a polymer having the material as the polymer main chaincan be also used. As the hole injecting material or the holetransporting material, inorganic compounds such as p-Si and p-SiC areusable.

The hole transporting layer can be formed by preparing a thin layer ofthe hole transporting material using a known method such as a vacuumdeposition method, a spin coat method, a casting method, an ink jetmethod, or an LB method. The thickness of the hole transporting layer isnot specifically limited, however, is ordinarily 5 to 5000 nm andpreferably 5 to 200 nm. The hole transporting layer may be composed of asingle layer structure containing one or two or more of the materialsmentioned above.

<<Electron Transporting Layer>>

The electron transporting layer contains a material having an electrontransporting ability, and in a broad sense an electron injecting layeror a hole blocking layer are included in an electron transporting layer.The electron transporting layer can be provided as a single layer or asplural layers.

An electron transporting material (which serves also as a hole blockingmaterial) used in a single electron transporting layer or in theelectron transporting layer closest to the cathode when plural electrontransporting layers are employed, may be a compound which has a functionof transporting electrons injected from a cathode to a light emittinglayer. The material used in the electron transporting layer can beoptionally selected from known compounds used as electron transportingmaterials. Examples of the material used in the electron transportinglayer include a nitro-substituted fluorine derivative, a diphenylquinonederivative, a thiopyran dioxide derivative, a carbodiimide, afluolenylidenemethane derivative, an anthraquinodimethane, an anthronederivative, and an oxadiazole derivative. Moreover, a thiadiazolederivative which is formed by substituting the oxygen atom in theoxadiazole ring of the foregoing oxadiazole derivative with a sulfuratom, and a quinoxaline derivative having a quinoxaline ring known as anelectron withdrawing group are also usable as the electron transportingmaterial. A polymer in which the material mentioned above is introducedin the polymer side chain or a polymer having the material as thepolymer main chain can be also used.

A metal complex of an 8-quinolynol derivative such as aluminumtris(8-quinolynol) (Alq), aluminum tris(5,7-dichloro-8-quinolynol),aluminum tris(5,7-dibromo-8-quinolynol), aluminumtris(2-methyl-8-quinolynol), aluminum tris(5-methyl-8-quinolynol), orzinc bis(8-quinolynol) (Znq), and a metal complex formed by replacingthe central metal of the foregoing complexes with another metal atomsuch as In, Mg, Cu, Ca, Sn, Ga or Pb, can be used as the electrontransporting material. Furthermore, a metal free or metal-containingphthalocyanine, and a derivative thereof, in which the molecularterminal is replaced by a substituent such as an alkyl group or asulfonic acid group, are also preferably used as the electrontransporting material. The distyrylpyrazine derivative exemplified as amaterial for the light emitting layer may preferably be employed as theelectron transporting material. An inorganic semiconductor such as n-Siand n-SiC may also be used as the electron transporting material in asimilar way as in the hole transporting layer.

The electron transporting layer can be formed employing the abovedescribed electron transporting materials and a known method such as avacuum deposition method, a spin coat method, a casting method, aprinting method including an ink jet method or an LB method. Thethickness of electron transporting layer is not specifically limited,however, is ordinarily 5 nm to 5 μm, and preferably 5 to 200 nm. Theelectron transporting layer may be composed of a single layer containingone or two or more of the electron transporting material.

<<Substrate>>

The organic EL element of the present invention is preferably providedon a substrate.

The substrate (also referred to as base plate, base or support) employedfor the organic EL element of the present invention is not limited tospecific kinds of materials such as glass and plastic, as far as it istransparent. Examples of the substrate preferably used include glass,quartz and light transmissible plastic film. Specifically preferred oneis a resin film capable of providing flexibility to the organic ELelement.

Examples of the resin film include films of polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polyethersulfone (PES),polyetherimide, polyetheretherketone, polyphenylene sulfide,polyarylate, polyimide, polycarbonate (PC), cellulose triacetate (TAC),cellulose acetate propionate (CAP). The surface of the resin film mayhave a layer of an inorganic or organic compound or a hybrid layer ofboth compounds.

The external light emission efficiency (external quantum efficiency) ofthe organic EL element of the present invention is preferably not lessthan 1%, and more preferably not less than 5% at room temperature.Herein, external quantum yield (%) is represented by the followingformula:External quantum yield (%)=(the number of photons emitted to theexterior of the organic electroluminescent element×100)/(the number ofelectrons supplied to the organic EL element)

A hue improving filter such as a color filter may be used in combinationor a color conversion filter which can convert emission light color froman organic EL element to multi-color employing a fluorescent compoundmay be used in combination. In the case where the color conversionfilter is used, the λmax of the light emitted from the organic ELelement is preferably not more than 480 nm.

<<Preparation of Organic EL Element>>

For one example, the preparation of the organic EL element, which hasthe following constitution will be described: Anode/Hole injectinglayer/Hole transporting layer/Light emitting layer/Electron transportinglayer/Electron injecting layer/Cathode.

A thin layer of a desired material for an electrode such as a materialof the anode is formed on a suitable substrate by a vacuum depositionmethod or sputtering method to prepare the anode, so that the thicknessof the layer is not more than 1 μm, and preferably within the range offrom 10 to 200 nm. Then the hole injecting layer, the hole transportinglayer, the light emitting layer, the electron transporting layer and theelectron injecting layer, which constitute the organic EL element, areformed on the resulting anode as organic compound thin layers.

As methods for formation of the thin layers, as the same as describedabove, there are a vacuum deposition method and a wet process (forexample, a spin coating method, a casting method, an ink jet method, anda printing method), however, a vacuum deposition method, a spin coatingmethod, an ink jet method and a printing method are preferably used,since a uniform layer without a pinhole can be formed. Different methodsmay be used for formation of different layers. When the vacuumdeposition method is used for the thin layer formation method, althoughconditions of the vacuum deposition differs due to kinds of materialsused, vacuum deposition is preferably carried out at a boat temperatureof from 50° C. to 450° C., at a degree of vacuum of from 10⁻⁶ to 10⁻²Pa, at a deposition speed of from 0.01 to 50 nm/second, and at asubstrate temperature of from −50 to 300° C. to form a layer with athickness of from 0.1 nm to 5 μm, preferably from 5 to 200 nm.

After these layers has been formed, a thin layer of a material for acathode is formed thereon to prepare a cathode, employing, for example,a vacuum deposition method or sputtering method to give a thickness ofnot more than 1 μm, and preferably from 50 to 200 nm. Thus, a desiredorganic EL element is obtained. It is preferred that the layers from thehole injecting layer to the cathode are continuously formed under onetime of vacuuming to obtain an organic EL element. However, on the wayof the layer formation under vacuum, a different layer formation methodby taking the layer out of the vacuum chamber may be inserted. When thedifferent method is used, the process is preferably carried out under adry inert gas atmosphere.

In the multicolor display of the present invention, the light emittinglayer only is formed using a shadow mask, and the other layers, besidesthe light emitting layer, are formed employing a vacuum depositionmethod, a casting method, a spin coat method or a printing method inwhich patterning employing the shadow mask is not required, since theselayers are common to all the pixels. When the light emitting layer onlyis formed by patterning, the layer formation, although not specificallylimited, is carried out preferably according to a vacuum depositionmethod, an ink jet method or a printing method. When a vacuum depositionmethod is used as the layer formation method, patterning of the layer ispreferably carried out employing a shadow mask.

Further, the organic EL element can be prepared in the reverse order, inwhich the cathode, the electron injecting layer, the electrontransporting layer, the light emitting layer, the hole transportinglayer, the hole injecting layer, and the anode are formed in that order.When a direct current voltage of 2 to 40 V is applied to thus obtainedmulticolor display, setting the anode as a +polarity and the cathode asa −polarity, light emission occurs. An alternating current may also beapplied to cause light emission. Arbitrary wave shape of alternatingcurrent may be used.

The display of the present invention can be used as a display device, adisplay, or various light emission sources. The display device or thedisplay, which employs three kinds of organic EL elements emitting ablue light, a red light and a green light can present a full colorimage.

Examples of the display device or the display include a television, apersonal computer, a mobile device or an AV device, a display for textbroadcasting, and an information display used in a car. The displaydevice may be used as specifically a display for reproducing a stillimage or a moving image. When the display device is used as a displayfor reproducing a moving image, the driving method may be either asimple matrix (passive matrix) method or an active matrix method.

Examples of an illuminator include a home lamp, a room lamp in a car, abacklight for a watch or a liquid crystal, a light source for boardingadvertisement, a signal device, a light source for a photo memorymedium, a light source for an electrophotographic copier, a light sourcefor an optical communication instrument, and a light source for anoptical sensor, however, are not limited thereto.

The organic EL element of the present invention may be an organic ELelement having a resonator structure. The organic EL element having aresonator structure is applied to a light source for a photo-memorymedium, a light source for an electrophotographic copier, a light sourcefor an optical communication instrument, or a light source for aphoto-sensor, however, its application is not limited thereto. In theabove application, a laser oscillation may be carried out.

<<Display>>

The organic EL element of the present invention can be used as a lampsuch as an illuminating lamp or a light source for exposure, as aprojection device for projecting an image, or as a display for directlyviewing a still image or a moving image. When the element is used in adisplay for reproducing a moving image, the driving method may be eithera simple matrix (passive matrix) method or an active matrix method. Thedisplay can present a full color image by employing three or more kindsof organic EL elements each emitting light with a different color. Amonochromatic color, for example, a white color can be converted to BGRcolors to form a full color image, employing a color filter. Further,employing a color conversion filter, light color emitted from theorganic EL element can be converted to another color or full color,where the λmax of the light emitted from the organic EL element ispreferably not more than 480 nm.

One example of the display containing the organic EL element of thepresent invention will be explained below employing Figures.

FIG. 1 is a schematic drawing of one example of a display containing anorganic EL element. FIG. 1 is a display such as that of a cellularphone, displaying image information due to light emission from theorganic EL.

A display 1 contains a display section A having plural pixels and acontrol section B carrying out image scanning based on image informationto display an image in the display section A.

The control section B is electrically connected to the display sectionA, transmits a scanning signal and an image data signal to each of theplural pixels based on image information from the exterior, and conductsimage scanning which emits light from each pixel due to the scanningsignal according to the image data signal, whereby an image is displayedon the display section A.

FIG. 2 is a schematic drawing of a display section A.

The display section A contains a substrate, plural pixels 3, and awiring section containing plural scanning lines 5 and plural data lines6. The main members of the display section A will be explained below. InFIG. 2, light from pixels 3 is emitted in the direction of an arrow.

The plural scanning lines 5 and plural data lines 6 of the wiringsection 2 each are composed of an electroconductive material, the lines5 and the lines 6 being crossed with each other at a right angle, andconnected with the pixels 3 at the crossed points (not illustrated).

The plural pixels 3, when the scanning signal is applied from thescanning lines 5, receive the data signal from the data lines 6, andemit light corresponding to the image data received. Provision of redlight emitting pixels, green light emitting pixels, and blue lightemitting pixels side by side on the same substrate can display a fullcolor image.

Next, an emission process of pixels will be explained.

FIG. 3 is a schematic drawing of a pixel.

The pixel contains an organic EL element 10, a switching transistor 11,a driving transistor 12, and a capacitor 13. When a pixel with a redlight emitting organic EL element, a pixel with a green light emittingorganic EL element, and a pixel with a blue light emitting organic ELelement are provided side by side on the same substrate, a full colorimage can be displayed.

In FIG. 3, an image data signal is applied through the data lines 6 fromthe control section B to a drain of the switching transistor 11, andwhen a scanning signal is applied to a gate of the switching transistor11 through the scanning lines 5 from the control section B, theswitching transistor 11 is switched on, and the image signal dataapplied to the drain is transmitted to the capacitor 13 and the gate ofthe driving transistor 12.

The capacitor 13 is charged according to the electric potential of theimage data signal transmitted, and the driving transistor 12 is switchedon. In the driving transistor 12, the drain is connected to an electricsource line 7, and the source to an organic EL element 10. Current issupplied from the electric source line 7 to the organic EL element 10according to the electric potential of the image data signal applied tothe gate.

The scanning signal is transmitted to the next scanning line 5 accordingto the successive scanning of the control section B, the switchingtransistor 11 is switched off. Even if the switching transistor 11 isswitched off, the driving transistor 12 is turned on since the capacitor13 maintains a charged potential of image data signal, and lightemission from the organic EL element 10 continues until the nextscanning signal is applied. When the next scanning signal is appliedaccording the successive scanning, the driving transistor 12 worksaccording to an electric potential of the next image data signalsynchronized with the scanning signal, and light is emitted from theorganic EL element 10.

That is, light is emitted from the organic EL element 10 in each of theplural pixels 3 due to the switching transistor 11 as an active elementand the driving transistor 12 each being provided in the organic ELelement 10 of each of the plural pixels 3. This emission process iscalled an active matrix process.

Herein, light emission from the organic EL element 10 may be emissionwith plural gradations according to image signal data of multiple valuehaving plural gradation potentials, or emission due to on-off accordingto a binary value of the image data signals.

The electric potential of the capacitor 13 may maintain till the nextapplication of the scanning signal, or may be discharged immediatelybefore the next scanning signal is applied.

In the present invention, light emission may be carried out employing apassive matrix method as well as the active matrix method as describedabove. The passive matrix method is one in which light is emitted fromthe organic EL element according to the data signal only when thescanning signals are scanned.

FIG. 4 is a schematic drawing of a display employing a passive matrixmethod. In FIG. 4, pixels 3 are provided between the scanning lines 5and the data lines 6, crossing with each other.

When scanning signal is applied to scanning line 5 according tosuccessive scanning, pixel 3 connecting the scanning line 5 emitsaccording to the image data signal. The passive matrix method has noactive element in the pixel 3, which reduces manufacturing cost of adisplay.

The materials of the present invention are also applicable to an organicEL element substantially emitting white light. White light is obtainedby mixing plural colors by simultaneously emitting plural colors fromplural light emitting materials. Examples of a combination of colors toobtain white light include: a combination containing three maximumemission wavelengths of three primary colors, namely, blue, green andred; and a combination containing a pair of maximum emission wavelengthsof two complementary colors, for example, blue-yellow and bluegreen-orange.

A combination for obtaining plural color lights may be a combination ofmaterials emitting fluorescence or phosphorescence (emitting dopants),or a combination of light emitting materials emitting fluorescence orphosphorescence, and colorants which emit light by absorbing lightemitted from those light emitting-materials as excitation light. For anorganic EL element emitting white light of the present invention,preferable is a combination of plural light emitting dopants.

Examples of a layer constitution to obtain plural color lights include:a method to incorporate plural emitting dopants in an emitting layer; amethod to provide plural emitting layers and emitting dopants havingdifferent emission wavelengths are incorporated one by one in eachemitting layer; and a method to provide matrix-arrayed minute pixelseach having different emission wavelength.

In the preparation process of the white light emitting organic ELelement of the present invention, patterning may be carried out whileforming each layer, if necessary, for example, by using a metal mask orby inkjet printing. Patterning may be carried out: only for electrodes,for electrodes and a light emitting layer, or for all the constitutinglayers.

Materials used for the light emitting layer are not specificallylimited, and, for example, in the case of preparing a backlight of aliquid crystal display, arbitrary materials may be selected and combinedfrom known light emitting materials including the iridium complexes orplatinum complexes of the present invention to generate white lightemission adjust the wavelength range corresponding to the CF (colorfilter) property.

The white light emitting organic EL element of the present invention maybe utilized as various light sources or an illuminator, for example, asa kind of lamp such as a home lamp, a room lamp in a car, or adeveloping lamp, or for a display such as a backlight for a liquidcrystal display.

It is also usable for a wide range of application, for example, as abacklight for a watch, a light source for boarding advertisement, asignal device, a light source for a photo memory medium, a light sourcefor an electrophotographic copier, a light source for an opticalcommunication instrument or a light source for an optical sensor, or inelectric home appliances using a display.

EXAMPLES

The present invention will now be explained using examples, however, thepresent invention is not limited thereto.

Example 1 Preparation of Organic EL Element 1-1

A pattern was formed on a substrate (100 mm×100 mm×1.1 mm) composed of aglass plate and a 100 nm ITO (indium tin oxide) layer (NA45 manufacturedby NH Technoglass Co., Ltd.) as an anode. Then the resulting transparentsubstrate having the ITO transparent electrode was subjected toultrasonic washing in i-propyl alcohol, dried with a dry nitrogen gasand subjected to UV-ozone cleaning for 5 minutes. Thus obtainedtransparent substrate was fixed on a substrate holder of a vacuumdeposition (evaporation) apparatus available on the market. Further, 200mg of α-NPD was placed in a first resistive heating molybdenum boat, 200mg of CBP as a host material was put in a second resistive heatingmolybdenum boat, 200 mg of bathocuproine (BCP) was placed in a thirdresistive heating molybdenum boat, 100 mg of D-1 was placed in a fourthresistive heating molybdenum boat, and 200 mg of Alq₃ was placed in afifth resistive heating molybdenum boat. The resulting boats were set inthe vacuum deposition apparatus.

The pressure in the vacuum tank was reduced to 4×10⁻⁴ Pa. Then, the boatcarrying α-NPD being heated by supplying an electric current to theboat, α-NPD was deposited onto the transparent substrate at a depositingrate of 0.1 nm/sec to form a hole transporting layer of a thickness of40 nm. After that, the boat carrying CBP and the boat carrying D-1 beingheated by supplying an electric current to both boats, CBP at adepositing rate of 0.2 nm/sec and D-1 at a depositing rate of 0.012nm/sec were co-deposited onto the resulting hole transporting layer toform a light emitting layer of a thickness of 40 nm. The temperature ofthe substrate at the time of the deposition was room temperature.Subsequently, the boat carrying BCP being heated by supplying anelectric current to the boat, BCP was deposited onto the resulting lightemitting layer at a depositing speed of 0.1 nm/sec to form an electrontransporting layer which also worked as a hole blocking layer of athickness of 10 nm. Further, the boat carrying Alq₃ being heated bysupplying an electric current to the boat, Alq₃ was deposited onto theresulting electron transporting layer at a depositing rate of 0.1 nm/secto form an electron injecting layer of a thickness of 40 nm. Thetemperature of the substrate at the time of the deposition was roomtemperature.

After that, a 0.5 nm thick lithium fluoride layer and a 110 nm thickaluminum layer were deposited on the resulting material to form acathode. Thus, Organic EL Element 1-1 was prepared.

Preparation of Organic EL Elements 1-2 to 1-20

Organic EL Elements 1-2 to 1-20 were prepared in the same manner asOrganic EL Element 1-1, except that CBP used as a host compound of theemitting layer in Organic EL Element 1-1 was replaced with the compoundslisted in Table 1 and that D-1 used as an emission dopant of theemitting layer in Organic EL Element 1-1 was replaced with the compoundslisted in Table 1. The structures of the compounds used above are shownbelow:

Evaluation of Organic EL Elements 1-1 to 1-20

Organic EL Elements 1-1 to 1-20 were evaluated in the manner describedbelow, and the results were summarized in Table 1.

(External Quantum Efficiency)

Electric current of 2.5 mA/cm² was supplied to each sample at 23° C. inan atmosphere of a dry nitrogen gas, and the external quantum efficiency(%) of each sample was measured. The external quantum efficiency (%) wascalculated from the date obtained by being measured through a spectralradiance meter CS-1000 produced by Konica Minolta Sensing Inc. Theresults of external quantum efficiency measurements in Table 1 weregiven as relative values when the value of external quantum efficiencyof Organic EL Element 1-1 was set to 100.

(Life)

A period in which an initial emission intensity of an organic EL elementdecreased to half of it was defined as a half-life period (τ0.5) andused as an index of the life of an organic EL element, the emissionintensity being measured by supplying a constant electric current of 2.5mA/cm² at 23° C. in an atmosphere of a dry nitrogen gas. A spectralradiance meter CS-1000 produced by Konica Minolta Sensing Inc. was usedfor the measurement of the life of an organic EL element. The results oflife measurements in Table 1 were given as relative values when thevalue of life of Organic EL Element 1-1 was set to 100.

TABLE 1 Organic External EL Host Guest Quantum Element Compound CompoundEfficiency Life Remarks 1-1 CBP D-1 100 100 Comparative 1-2 CBP D-3 98101 Comparative 1-3 H-1 D-1 165 129 Inventive 1-4 H-1 D-2 163 120Inventive 1-5 H-1 D-3 155 125 Inventive 1-6 H-1 D-25 147 115 Inventive1-7 H-1 D-40 144 123 Inventive 1-8 H-1 D-48 150 145 Inventive 1-9 H-1D-49 148 151 Inventive 1-10 H-8 D-1 178 119 Inventive 1-11 H-8 D-2 180120 Inventive 1-12 H-8 D-3 171 130 Inventive 1-13 H-8 D-48 159 139Inventive 1-14 H-8 D-49 155 145 Inventive 1-15 H-12 D-1 160 138Inventive 1-16 H-12 D-49 162 140 Inventive 1-17 H-13 D-1 161 128Inventive 1-18 H-13 D-49 159 139 Inventive 1-19 Comparative 1 Ir-12 15051 Comparative 1-20 H-1 Ir-12 160 67 Comparative

The results shown in Table 1 revealed that the organic EL elements ofthe present invention exhibits high external quantum efficiencies andlong lives.

Example 2

A 20 mm×20 mm pattern of transparent electrode was formed on thetransparent substrate of Example 1, on which 50 nm thickness of α-NPDwas formed as a hole injection/transport layer as described in Example1, and a 30 nm thickness of a light emitting layer was formed, which wasprepared as follows: a boat carrying H-1, a boat carrying D-1 and a boatcarrying Ir-9 were independently heated by supplying an electric currentso that the ratio of depositing rates of H-1: D-1: Ir-9 were adjusted to100:5:0.6.

Subsequently, 10 nm of BCP was formed as an electron transport layer and40 nm of Alq₃ was formed as an electron injecting layer.

Then, the vacuum tank was opened and a stainless steel mask having asquare hole of almost the same dimension as the transparent electrodewas placed on the electron injecting layer to form 0.5 nm thickness oflithium fluoride as a cathode buffer layer and 110 nm of aluminum as acathode, by vacuum evaporation (vacuum deposition).

A plane lamp was prepared by sealing the organic EL element as shown inFIGS. 5 and 6. When the lamp was turned on, emission of almost whitelight was observed, showing that the plane lamp of the present inventionis applicable as an illuminator. When the host compound was changed toother compound of the present invention, similarly, emission of whitelight was observed. In FIGS. 5 and 6, 101 represents a transparentsubstrate, 102 represents a glass cover, 105 represents a cathode, 106represents an organic EL layer, 107 represents a substrate having atransparent electrode, 108 represents nitrogen gas and 109 represents adessicant.

Example 3 Preparation of Full Color Display

(Preparation of Blue Light Emitting Element)

Organic EL element 1-3 was used as a blue light emitting element.

(Preparation of Green Light Emitting Element)

A green light emitting element was prepared in the same manner asOrganic EL element 1-3 except that CBP was used as a host compound andIr-1 was used as a dopant.

(Preparation of Red Light Emitting Element)

A red light emitting element was prepared in the same manner as OrganicEL element 1-3 except that CBP was used as a host compound and Ir-9 wasused as a dopant.

The above red, green and blue light emitting organic EL elements werejuxtaposed on the same substrate to prepare a full color display drivenby an active matrix method, illustrated in FIG. 1. In FIG. 2, aschematic drawing of only display section A is shown. Namely, on thesame substrate, a wiring section containing plural scanning lines 5 andplural data lines 6, and juxtaposed plural pixels 3 (pixels emitting redlight, pixels emitting green light and pixels emitting blue light) areprovided. The plural scanning lines 5 and plural data lines 6 of thewiring section are composed of an electroconductive material. Thescanning lines 5 and the data lines 6 are crossing with each other at aright angle to form a lattice, and connected to the pixels 3 at thecrossed points (not illustrated). The plural pixels 3 are driven by anactive matrix method in which each pixel contains an organic EL elementemitting a corresponding color light and active elements including aswitching transistor and a driving transistor. When scanning signals areapplied through the scanning lines 5, image data signals are receivedthrough data lines 6, and emission occurs according to the receivedimage data. By juxtaposing red light emitting pixels, green lightemitting pixels, and blue light emitting pixels side by side on the samesubstrate, a full color display is prepared.

By driving the full color display, it was found that a bright fullcolor-moving picture with high luminance, and long life was obtained.

Example 4 Preparation of Illuminator

An illuminator was prepared by covering each non-emitting surface of theorganic EL elements emitting blue light, green light and red light witha glass case. Thus prepared illuminator was found to be a thin filmwhite light emitting illuminator exhibiting high emission efficiency andlong life. FIG. 5 shows a schematic illustration of the illuminator, andFIG. 6 shows a cross-section of the illuminator. Organic EL element 101was covered with glass cover 102.

105 represents a cathode, 106 represents an organic EL layer, 107represents a glass substrate having a transparent electrode. Insideglass cover 102 is filled with nitrogen gas 108 and desiccant 109 isprovided.

The range of color reproducibility was evaluated by using the organic ELelement of the present invention in combination with a commerciallyavailable color filter for a display, and it was found that a wide rangeof color reproducibility was observed, indicating that the organic ELelement of the present invention exhibits an excellent property in colorreproducibility.

What is claimed is:
 1. An organic electroluminescent element comprisingan anode and a cathode having therebetween a light emitting layer,wherein the light emitting layer comprises a guest compound representedby one of Formulae (A-1) through (A-9) and a host compound representedby Formula (1):

wherein Ra represents an alkyl group, an aromatic hydrocarbon group or aheteroaromatic group, Rb and Rc each represent a hydrogen atom or asubstituent selected from the group consisting of an alkyl group, anaromatic hydrocarbon group, an alkoxy group and a halogen atom; A1represents a benzene ring or a pyridine ring; wherein a plurality of A1are the same or different, a plurality of Ra are the same or different,a plurality of Rb are the same or different and a plurality of Rc arethe same or different, in each of Formulae (A-1) through (A-9);

wherein Ra₁ represents a phenyl group; R₁ and R₂ each represent a phenylgroup or a pyridyl group; R₅ represents a substituent selected fromGroup 1; and n1, n2 and n5 each represent an integer of 0 to 4, whereinthe Group 1 substituent is selected from the group consisting of analkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, anaromatic hydrocarbon group, an aromatic heterocycle group, a heterocyclegroup, an alkoxy group, a cycloalkoxyl group, an aryloxy group, analkylthio group, a cycloalkylthio group, an arylthio group, analkoxycarbonyl group, an aryloxycarbonyl group, a sulfamoyl group, anacyl group, an acyloxy group, an amide group, a carbamoyl group, anureido group, a sulfinyl group, an alkylsulfonyl group, an arylsulfonylgroup, an amino group, a halogen atom, a hydrofluorocarbon group, acyano group, a nitro group, a hydroxyl group, a mercapto group and asilyl group.
 2. The organic electroluminescent element of claim 1,wherein the aromatic hydrocarbon ring represented by A1 in any one ofFormula (A-1) through (A-9) is a benzene ring.
 3. The organicelectroluminescent element of claim 1 which emits blue light.
 4. Theorganic electroluminescent element of claim 1 which emits white light.5. A display comprising the organic electroluminescent element ofclaim
 1. 6. An illuminator comprising the organic electroluminescentelement of claim
 1. 7. A display comprising the illuminator of claim 6and a liquid crystal cell as a display means.
 8. The organicelectroluminescent element of claim 1, wherein R₅ in Formula (1)represents an aromatic hydrocarbon group or an aromatic heterocyclegroup.
 9. An organic electroluminescent element comprising an anode anda cathode having therebetween a light emitting layer, wherein the lightemitting layer comprises a guest compound represented by one of Formula(B-1) through (B-3) and a host compound represented by Formula (1):

wherein Ra represents an alkyl group or an aromatic hydrocarbon group;Rb, Rc, Rb₁ and Rc₁ each represent a hydrogen atom; A1 represents abenzene ring; M represents Ir; Formula (1)

wherein Ra₁ represents a phenyl group; R₁ and R₂ each represent a phenylgroup or a pyridyl group, R₅ represents a substituent selected fromGroup 1; and n1, n2 and n5 each represent an integer of 0 to 4, whereinthe Group 1 substituent is selected from the group constituting of analkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, anaromatic hydrocarbon group, an aromatic heterocycle group, a heterocyclegroup, an alkoxy group, a cycloalkoxyl group, an aryloxy group, analkylthio group, a cycloalkylthio group, an arylthio group, analkoxycarbonyl group, an aryloxycarbonyl group, a sulfamoyl group, anacyl group, an acyloxy group, an amide group, a carbamoyl group, anureido group, a sulfinyl group, an alkylsulfonyl group, an arylsulfonylgroup, an amino group, a halogen atom, a hydrofluorocarbon group, acyano group, a nitro group, a hydroxyl group, a mercapto group and asilyl group.
 10. An organic electroluminescent element comprising ananode and a cathode having therebetween a light emitting layer, whereinthe light emitting layer comprises a guest compound represented by oneof Formulae (C-1) through (C-3) and a host compound represented byFormula (I):

wherein Ra represents an alkyl group or an aromatic hydrocarbon group;Rb, and Rc each represent a hydrogen atom or an alkyl group; A1represents a benzene ring; M represents Ir;

wherein Ra₁ represents a phenyl group; R₁ and R₂ each represent a phenylgroup or a pyridyl group, R₅ represents a substituent selected fromGroup 1; and n1, n2 and n5 each represent an integer of 0 to 4, whereinthe Group 1 substituent is selected from the group consisting of analkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, anaromatic hydrocarbon group, an aromatic heterocycle group, a heterocyclegroup, an alkoxy group, a cycloalkoxyl group, an aryloxy group, analkylthio group, a cycloalkylthio group, an arylthio group, analkoxycarbonyl group, an aryloxycarbonyl group, a sulfamoyl group, anacyl group, an aryloxy group, an amide group, a carbamoyl group, anureido group, a sulfinyl group, an alkylsulfonyl group, an arylsulfonylgroup, an amino group, a halogen atom, a hydrofluorocarbon group, acyano group, a nitro group, a hydroxyl group, a mercapto group and asilyl group.
 11. The organic electroluminescent element of claim 10,wherein R₅ in Formula (1) represents an aromatic hydrocarbon group or anaromatic heterocycle group.